38 
THE VOYAGE OF H.M.S. CHALLEHGEE. 
Botrylloides, Milne-Edwards. 
Botryllus, Savigny, M4moires, &c., 1816. In part. 
Botrylloides, Milne-Edwards, Observations, &c., 1842. In part. 
Botrylloides, Forbes and Hanley, British Mollusca, 1853. In part. 
Botrylloides, Alder, Ann. and Mag. Nat. Hist., 1863. In part. 
Botrylloides, Giard, Kecberches, &c., 1872. In part. 
Botrylloides, Della Valle, Contribuzioni, &c., 1877. In part. 
Botrylloides, von Drasche, Synascidien, &c., 1883, p. 15. 
Colony thin, incrusting, and usually gelatinous. 
Systems elliptical, or elongated, forming branched and sometimes anastomosing lines. 
Ascidiozooids cylindrical, with the apertures placed near one another on the 
anterior end. 
Test soft and gelatinous, never much thickened, penetrated by many vessels. 
Branchial Sac long and well developed. 
Alimentary Canal placed alongside the branchial sac at its posterior end. 
' Reproductive Organs placed on both sides of the body near the posterior end. 
This genus is distinguished from Botryllus and from Polycyclus by the shape of the 
systems, which may be of any form so long as they are not regular and circular ; and 
from Sarcobotrylloides and Polycyclus by the colony forming a thin crust and not a solid 
mass. In this restricted sense Botrylloides has been used by von Drasche, while all other 
writers since Milne-Edwards (1842) include in it forms with a thickened test and 
massive colonies {Sarcobotrylloides, von Drasche). 
Savigny, as Giard has pointed out, really, indicated this genus in 1816 by dividing 
his species of Botryllus into sections, of which his first tribe corresponds exactly to Milne- 
Edwards’ Botrylloides. No one, however, seems to have considered the group of species 
worthy of generic rank until Milne-Edwards in 1842 founded the genus Botrylloides for 
-Savigny’s first tribe of Botrylli and some new species which he described and figured in 
his great work on the Compound Ascidians of the English Channel. Since then many 
new species have been described, chiefly by Alder, Giard, and Della Valle. 
I have adopted von Drasche’s separation of the thin incrusting forms from those 
producing thick masses [Sarcobotrylloides), as it is certainly a convenient distinction and 
one which deserves to be recognised as much as does the similar character distinguishing 
Botryllus from Polycyclus. 
The systems of Botrylloides are usually very irregular, but have a characteristic 
appearance (see Fig. 8, D and E, j). 39, and PI. I. Figs. 1, 4). They are formed generally 
of several lines extending in different directions from a common cloaca, and in some 
cases branching and anastomosing. The Ascidiozooids border these lines, and are 
therefore placed in more or less parallel double rows. The following diagrams (Fig. 8) 
